A variety of gas ignition controls are known and generally include apparatus constructed of discrete components for effecting a single, predetermined control sequence tailored to a specific application. Such gas ignition systems typically include a relay which is energized in response to a thermostatic demand for heat and for actuating a pilot gas valve, a spark generating circuit for igniting the pilot gas either coincidently with the energization of the pilot valve or within a predetermined time thereafter, a flame sensing probe for detecting the presence of a pilot flame and an output relay section for energizing a main fuel valve upon the detection of the pilot flame. Refinements of this fundamental system may include a pair of electromagnetic relays which are required to be operated in a particular sequence upon each reception of a thermostatic demand for heat. The sequential operation of these relays is effective for verifying the integrity of certain circuit components. Examples of such gas ignition systems are shown and described in U.S. Pat. Nos. 4,077,762 and 4,178,149. While these gas ignition systems have heretofore been satisfactory, they have failed to appreciate the manner in which a microprocessor may be utilized therein to continually monitor and verify the integrity of certain circuit components and to provide a degree of application flexibility heretofore unknown.
In particular, these earlier devices have failed to appreciate how a microprocessor-based control apparatus may be programmably configured with any one of a variety of control strategies whereby the apparatus may be readily adapted to a variety of gas fueled furnaces, each presenting a different control requirement.
A microprocessor-based apparatus for controlling the operation of a combustion fuel burner and which makes advantageous use of a synchronizing signal for monitoring the integrity of certain circuit components, which may incorporate one or more input and output stages and which is adaptable to conduct its control sequences in accordance with predetermined lapses of time rather than upon the occurrence of predetermined events would be a distinct advance in the art.